How to inset a curve into section of circle?
One way to obtain the result you want could be to select the edges in the mesh I selected in the image below and simply click on "Subdivide" in the Tools panel on the left. You should obtain something like the second image, which looks similar to the one you posted in the comments. Remember that you have to do this before using the array modifier, so either hide it by clicking on the eye icon in the modifier panel or delete it and make a new one from the beginning, after you obtained the result you want with the original mesh.